Communication system with variable output supply current

ABSTRACT

A system including a bus and a plurality of devices coupled thereto and configured to communicate with each other via the bus. The system further includes a power supply coupled to the bus, to power to the plurality of devices via the bus and to detect an event, and in response, alternately supply power to the plurality of devices via the bus at a first current level or at a lesser second current level. This allows additional devices to be used on a bus, even where the total power consumption of the devices would normally exceed a maximum defined by a bus architecture. This also helps allow a single gauge of wire to be used throughout a bus network (even where long lengths of wire are required) while still providing sufficient power to the devices connected to the bus.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of, and claims priority to,U.S. patent application Ser. No. 13/161,340, filed Jun. 15, 2011 andentitled “SYSTEM BUS WITH VARIABLE OUTPUT POWER SUPPLY”, which is acontinuation of, and claims priority to, U.S. patent application Ser.No. 13/161,314, now U.S. Pat. No. 8,694,817, filed Jun. 15, 2011 andentitled “BUS NETWORK”, the contents of both of which are incorporatedherein by reference.

BACKGROUND

Bus networks are used in a variety of fields and applications tointerconnect devices and allow communication, power transmission, andother functionality. One such bus network is known as a DigitalAddressable Lighting Interface (DALI), which is a bus architecturestandard used in controlling devices in a building (such as sensors,lighting devices, and shades). DALI provides a two-wire bus that allowspower to be supplied to, and communication between, devices on the bus.In the DALI architecture, the presence of voltage indicates a firststate (i.e., a logical “1”), while the shorting of the two wires by anydevice on the bus indicates a second state (i.e., a logical “0”). Inthis manner, devices can use the two-wire DALI bus to communicate witheach other.

In some bus network architectures, including DALI, the amount of powerthat can be supplied to devices on the bus may be limited by thearchitecture specification, which may in turn limit the number ofdevices that can be connected to the bus. In the DALI architecture, forexample, power is typically supplied at 16.5V (22.5V maximum) with acurrent limit of 250 mA. According to the DALI specification, up tosixty-four devices can theoretically be coupled to a DALI bus, but manyDALI-compatible devices can draw, for example, up to 40 mA each,effectively limiting the number of such devices that can actually beconnected to the bus.

Similarly, the impedance of the bus wiring can limit the number ofdevices that can be connected to a bus. For example, DALI bus networksare often deployed in large buildings, requiring long lengths of wiringto be run to the devices in the building. Conventional DALI networks uselower gauge (i.e., thicker) wires as the bus gets longer, which is notonly more expensive than higher gauge wire, but also increases theoverall complexity of installation. Installers of such buses may have towork with multiple spools of wire, which can increase the time and costto install a bus network.

Embodiments in this disclosure address these and other issues.

SUMMARY

Among other things, embodiments in this disclosure help allow additionaldevices to be used on a bus, even where the total power consumption ofthe devices would normally exceed a maximum defined by a busarchitecture. Furthermore, various embodiments help allow a single gaugeof wire to be used throughout a bus network (even where long lengths ofwire are required) while still providing sufficient power to the devicesconnected to the bus.

A system according to various embodiments of the disclosure includes abus and a plurality of devices coupled to the bus, the devicesconfigured to communicate with each other via the bus. The systemfurther includes a power supply coupled to the bus, the power supply forsupplying power to the plurality of devices via the bus. The powersupply is configured to detect an event, and in response to the event,alternately supply power to the plurality of devices via the bus at afirst current level or at a second current level, the second currentlevel less than the first current level.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the disclosure, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the embodiments of the presentdisclosure may be derived by referring to the detailed description andclaims when considered in connection with the following illustrativefigures.

FIG. 1 illustrates an exemplary DALI bus network.

FIGS. 2 and 3 depict exemplary circuits for use in power supplies inaccordance with various embodiments.

FIG. 4 illustrates the input stage of a conventional DALI device.

FIG. 5 illustrates an exemplary input stage for a DALI device inaccordance with various embodiments.

FIG. 6 illustrates an exemplary circuit for use in a DALI deviceaccording to various embodiments.

FIG. 7 depicts an exemplary bus in accordance with various embodiments.

FIG. 8 illustrates a typical communications timing diagram for DALIdevices.

DETAILED DESCRIPTION

While exemplary embodiments in this disclosure are described inconjunction with the DALI bus architecture, this disclosure may be usedin conjunction with any other suitable bus architecture.

The detailed description of exemplary embodiments herein makes referenceto the accompanying drawings and pictures, which show the exemplaryembodiment by way of illustration and its best mode. While theseexemplary embodiments are described in sufficient detail to enable thoseskilled in the art to practice the disclosure, it should be understoodthat other embodiments may be realized and that logical and mechanicalchanges may be made without departing from the spirit and scope of thedisclosure. Thus, the detailed description herein is presented forpurposes of illustration only and not of limitation. For example, thesteps recited in any of the method or process descriptions may beexecuted in any order and are not limited to the order presented.Moreover, any of the functions or steps may be outsourced to orperformed by one or more third parties. Furthermore, any reference tosingular includes plural embodiments, and any reference to more than onecomponent may include a singular embodiment.

In the detailed description herein, references to “an embodiment”, “anembodiment”, “an example embodiment”, etc., indicate that the embodimentdescribed may include a particular feature, structure, orcharacteristic, but every embodiment may not necessarily include theparticular feature, structure, or characteristic. Moreover, such phrasesare not necessarily referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with an embodiment, it is submitted that it is within theknowledge of one skilled in the art to effect such feature, structure,or characteristic in connection with other embodiments whether or notexplicitly described. After reading the description, it will be apparentto one skilled in the relevant art(s) how to implement the disclosure inalternative embodiments.

In various embodiments, the methods described herein are implementedusing the various particular machines described herein. The methodsdescribed herein may be implemented using the below particular machines,and those hereinafter developed, in any suitable combination, as wouldbe appreciated immediately by one skilled in the art. Further, as isunambiguous from this disclosure, the methods described herein mayresult in various transformations of certain articles.

Exemplary System

FIG. 1 illustrates an exemplary DALI bus network 100. In this example,the bus network 100 includes a power supply 110, control device 120, anda plurality of devices 130 (also referred to as “nodes”) connected via atwo-wire bus 140.

Power Supply 110

DALI devices can be damaged if, during communication, they attempt toshort power supplied at current levels above the 250 mA limit specifiedin the DALI standard. In an embodiment, the power supply 110 isconfigured to detect an event, and, in response to the event,alternately supply power to the devices 130 at a higher or lower currentlevel via the bus 140. The power supply 110 may be configured toalternately supply power at any number of different levels of voltageand/or current. In one exemplary embodiment, the power supply 110 isconfigured to provide power at a first current limit of 750 mA whendevices/nodes are not communicating, and then supply power at a secondcurrent level of 250 mA to allow devices 130 on the bus 140 tocommunicate without damage.

The power supply 110 may be configured to supply power at varyingcurrent and/or voltage levels in response to any type of event. In thiscontext, an “event” may include, for example, any number of measuredelectrical characteristics (e.g., current, voltage, impedance) as wellas signals from other devices. In an embodiment, the power supply 110may detect an event that includes a decrease in impedance for one ormore of the devices 130. In DALI systems, the impedance for a device 130on the bus 140 decreases when the device 130 shorts the bus 140 tocommunicate. In such cases, the power supply 110 can decrease thecurrent level of the power supplied to the devices 130 when theimpedance of a device 130 drops (indicating it is communicating) andthen increase the current level of the power supplied to the devices 130when the impedance increases (indicating the device 130 is no longercommunicating).

In addition, or as an alternative, to detecting a change in impedance,the power supply 110 may be configured to detect a change in the currentdrawn by a device 130. In an embodiment, the power supply 110 isconfigured to supply power to the devices 130 on bus 140 at a decreasedcurrent level in response to detecting an increase in current drawn byone or more of the devices 130 (e.g., when the device 130 iscommunicating on the bus 140). The power supply 110 is furtherconfigured to supply power at an increased level upon detecting adecrease in current drawn by the device 130 (e.g., when the device 130is no longer communicating).

The power supply 110 may be configured to supply power at varyingcurrent levels in any suitable manner. In one exemplary embodiment, thepower supply 110 includes a component known as a “pass element” (such asa transistor) to increase and decrease the output voltage of the powersupply 110. The pass element dissipates power according to the productof the magnitude of the voltage reduction multiplied by the current itis delivering to the bus 140, thus the lower the output voltage, thehigher the dissipation. For example, if a 16.5V supply must drop down to0.5V to limit current to 250 mA, it dissipates 4 W of power.

The power supply 110 may be configured to perform a technique called“fold-back” to dynamically change the current limit as a function of theoutput voltage. In an embodiment, a power supply 110 is coupled to aDALI bus network 140 and is configured to detect an increase in currentdrawn by a node 130 attempting to communicate (i.e., by “shorting” thebus 140). The power supply 110 lowers its output voltage in response andlowers its current limit as well. As the node 130 continues to short thebus 140, the power supply 110 further reduces the voltage. For example,the power supply 110 may be configured to provide a current of 250 mA ata voltage of 6.5V (the maximum voltage allowed by the DALI standard as alogical zero).

In some cases, the nodes 130 may briefly see a current higher than theirdesign limit as the power supply 110 detects the event. However, thepower supply 110 can be configured to quickly (i.e., withinmicroseconds, in some cases) switch to providing power at a loweredcurrent level, thereby preventing component damage due to sustainedexcessive current. The power supply 110 may be configured to supplypower at an increased or decreased current level for any suitable periodof time (e.g., for the duration of communication between nodes tofurther reduce the frequency at which the node sees brief currents abovetheir design limit).

The power supply 110 can be configured to alter current levels over anysuitable period of time. In some embodiments, for example, currentlevels may be switched over a relatively short (e.g., withinmicroseconds or less) period of time. Among other things, this helpsreduce the amount of time a device 130 is shorting high current levelsand helps to avoid damage to the device 130 as a result.

In other embodiments, current levels may be altered over a relativelylonger period of time. In one exemplary embodiment, the power supply 110is configured to provide a dynamic current limit. Power supply 110 isconfigured to slowly (e.g., over about 10 mS) adjust its current limitto just above the instantaneous current. In an embodiment, if thecurrent rapidly increases (e.g., due to a node 130 shorting the bus140), the power supply will limit the current by lowering its outputvoltage for the duration of a logical zero. In an embodiment, the powersupply 110 provides the steady base current to the nodes 130 but doesnot allow sudden increases due to a node 130 shorting the bus. Thishelps to protect the “shorting” node 130 from experiencing excessivecurrent beyond its design limit and being damaged as a result.

In some embodiments, the power supply 110 may be configured to detect anevent that includes a change in the rate at which current is drawn byone or more of the devices 130. The current drawn by the devices 130 canbe monitored for sudden increases as an indicator that a node 130 isattempting to communicate. The DALI standard dictates that a node doesnot instantaneously short the current but requires the node to ramp upthe current within well defined boundaries to help reduceelectromagnetic emissions. Typically, an increase in current drawn by adevice 130 of 250 mA within 100 us is indicative that the node 130 isattempting to communicate.

The rate of change in current draw by a device 130 can be detected bythe power supply 110 in any suitable manner. In an embodiment, currentfrom the bus 140 is fed into a high-pass filter (which removes slowchanges in the current waveform) and the remaining signal (whichmeasures fast changes) is compared against a threshold. Exceeding thethreshold is indicative of a certain rate of current increase andthereby of a node 130 attempting communication. In response, the powersupply 110 can switch to supplying power at a lower current level toavoid damaging the devices 130 during communication.

In an embodiment, the event detected by the power supply 110 may includereceiving an indicator (e.g., from the control device 120 or one or moreof the devices 130) to supply current at a particular level. Among otherthings, this allows the power supply 110 to quickly and/or preemptivelyswitch from supplying current at one level to another before a device130 shorts the bus 140 for communication, and to supply a higher currentlevel when there is no communication between the devices 130.

FIG. 2 illustrates an exemplary circuit for use in a power supply 110.In an embodiment, circuit 200 includes a microcontroller 205 configuredto switch between two distinct current limits via digital output 210. ADC voltage is received at the input of the circuit 245 and passedthrough a voltage regulator 240, which helps maintain voltage output tomicrocontroller 205 and resister network 215 at a constant level.Resistor network 215 converts the signal from the digital output 210into one of two distinct voltage levels, which is directed into thepositive input of an operational amplifier 220. Current sensor 225provides a signal to the negative input of the operational amplifier220. If the actual current is higher than the limit programmed by themicrocontroller 205, the output from the operational amplifier 220drops, thereby increasing the impedance of the pass transistor 230, andin turn reducing the output current to the programmed limit at 235.

FIG. 3 depicts another exemplary circuit that may be used in conjunctionwith a power supply according to aspects of this disclosure. In anembodiment, circuit 300 includes the same components as circuit 200.Additionally, communication detector 310 (including a high-pass filtercoupled to a comparator), voltage feedback 320, and current feedback 330provide input to the microcontroller 205.

In addition to the functionality of circuit 200 described above, circuit300 is configured to detect communication between nodes 130. As a node130 attempts to communicate, the current it draws will suddenlyincrease. This increase is detected by the high pass filter/comparatorof the communications detector 310 and signaled to the microcontroller205. In turn, the microcontroller 205 will change the digital output210, thereby switching the power supply from a nominal current into, forexample, a relatively low current mode (such as 50 mA).

Among other things, circuit 300 helps nodes 130 communicate even whenthe bus impedance due to long wire lengths is relatively high. Forexample, as a communicating node 130 shorts the bus 140, power supply110 switches into a low current mode and the output voltage will drop tolevels that represent a logical zero. As the communicating node 130releases the short, the output voltage will suddenly rise (although notnecessarily high enough to represent a logical one). The increase involtage is signaled to the microcontroller 205 via voltage feedback 320.In response, the microcontroller 205 will increase the current limitagain, thereby returning the bus 140 to a logical one condition.

Control Device 120

In the exemplary system 100, the control device 120 can be configured tofacilitate communication between devices 130, interface with the powersupply 110 to control the current levels of power supplied to the bus140, and/or perform other functionality. In an embodiment, the controldevice 120 may function as a bus arbiter to declare the bus free for anynode 130 to commence communication (rather than instructing a specificnode to respond). Any node 130 may be configured to initiate a commandto any other node. In an embodiment, the control device 120 isconfigured to monitor communications between nodes 130, and to indicateto the power supply 110 to supply power at a particular current level.In this way, the control device 120 can preemptively instruct the powersupply 110 to switch to a lower current limit before a DALI device 130attempts to short the bus 140.

In an embodiment, control device 120 is coupled to the power supply 110,and interprets the current waveform (rather than voltages) in order toretrieve communications from devices 130. The control device 120 may beconfigured to take timing requirements (the known duration of individualbits) into account to filter out erroneous fluctuations in currentduring communication between the nodes 130. Alternatively, the currentdraw may be digitized and be processed further. Increases and decreasesin current may be assigned probabilities of being a positive or negativetransition and the probability of successive transitions collectivelymake up the probability of a particular bit sequence. Possible bitsequences may be processed in parallel and the highest probability pathshall win. In this manner, the control device 120 may operate inconjunction with the power supply 110 to allow the control device 120 toreceive responses from nodes 130 despite high wiring impedance.

Devices 130

Devices 130 (or “nodes”) receive power and communicate via the bus 140.Embodiments of this disclosure may operate in conjunction with anynumber and type of different devices on a bus. In the exemplaryembodiment of the DALI bus network 100 depicted in FIG. 1, the devices130 may include any type of DALI-compatible device, such as lightingdevices, sensors, and/or shades. A typical input stage of a conventionalDALI device is shown in FIG. 4. In this configuration, input stage 400provides optical isolation between the communication bus 140 andperipheral functions of device 130. In particular, power to device 130is not obtained from communication bus 140.

FIG. 5 depicts an exemplary embodiment of a DALI node 500 in accordancewith various aspects of this disclosure. In an embodiment, node 500comprises an input stage that includes a capacitor 505 (or other energystorage device) and a rectifier 510. The rectifier 510 prevents currentfrom flowing out of the storage device 505 back onto the bus 140, andtherefore the node will only consume current if the bus voltage ishigher than the voltage in the storage device 505. In other words, thecapacitor 505 can be charged up to the nominal voltage of the bus 140during periods of a logical one, and deplete somewhat during periods oflogical zeros. Typically, the node 500 will consume no current once thebus voltage drops a few volts below the typical bus voltage. Forexample, the bus voltage may usually be 16.5V (that is, during thelogical one). Below 15V, the node may consume no current, depending onthe configuration of the capacitor 505 and other factors. Power supply515 regulates the voltage of capacitor 505 to provide a constant supplyvoltage to the microcontroller and peripherals 520 of node 500.Peripherals may include circuitry to create a dimming signal to anexternal ballast. Transceiver 525 is coupled to the communication bus infront of rectifier 510 such that it is not subject to the signalfiltering introduced by capacitor 505.

During a logical one, the power supply 110 may output a nominal voltagewith a current limit of, for example, 750 mA. Preemptively, asfacilitated by a control device 120, or in response to an event, asexplained above, the power supply 110 can reduce the current and/orvoltage. In an embodiment, the power supply 110 is configured topreemptively reduce its output current to about 250 mA. In turn, theoutput voltage drops until the nodes collectively consume no more thansaid 250 mA. In this example, power supply 110 reduces its output toabout 15V. These levels are still considered a logical one by the nodes130, yet a node 130 that wishes to communicate by shorting the bus 140need only short 250 mA (a safe current level for a DALI node) instead of750 mA (an unsafe current level). Other nodes 130 may be configured todetect this low bus voltage and interpret it as a logical zero. In thismanner, nodes 130 with a rectifier and capacitor at their input stagehelp the power supply 110 create two modes of operation: A high currentdelivery mode and a lower, safer mode for DALI devices.

FIG. 6 illustrates an exemplary power supply circuit for a node 130 inaccordance with various embodiments. In an embodiment, the power supplycircuit 600 can electronically reduce the current draw for the node (tozero in some cases).

In operation, R12 biases D8 to generate a stable voltage at the base ofQ9. Q9 acts as an emitter-follower and provides a stable supply voltage+V to the microcontroller of the node (not shown), while C7 filters thesupply voltage. R9, Q14 and R16 form a constant current source whichlinearly charges C6. When the bus 140 is in the logical zero state, C6supplies a stable voltage to the microcontroller via D1, R12, D8, Q9 andC7.

Q7 allows the current source to be turned on and off. R36 biases Q7 inthe on-state. R16 allows base current through Q14B, turning it on, sothat C6 can charge. Q14A monitors the charge current via R9 and limitsit to approximately 0.7V divided by R9. Once the microcontroller hasbooted up, it can control the current source via the “Charge Control”output. Lowering this pin to GND turns Q7 off, which in turn turns Q14Boff and thereby removes the charging current into C6.

In an embodiment, circuit 600 allows the current consumption of a groupof DALI nodes 130 such that the nodes 130 collectively consume less than250 mA if their supply voltage is below a certain voltage. The nodes 130in an embodiment can thereby demonstrate similar behavior to nodeshaving a rectifier/capacitor input stage as described above. The powersupply 110 can then be preemptively switched from a higher current limitto a lower current limit (here 250 mA), thereby protecting the DALInodes which can only safely short the 250 mA current level or less.

In an embodiment, rather than activating the circuit 600 based on thenode's supply voltage, the node can activate the circuit when othernodes are attempting to communicate. Similarly, control device 120signals power supply 110 to switch to a lower current limit when othernodes 130 are attempting to communicate. Since nodes 130 have reducedtheir current consumption simultaneously by activating the circuit 600,the lower current limit of power supply 110 is temporarily sufficient tosupply the required current. Any DALI node 130 that wishes tocommunicate is protected and is only required to short the 250 mAcurrent level. Additionally, this allows groups of nodes to collectivelyalter their current draw to help facilitate communication between nodesat safe current levels, even if there is a relatively high level ofimpedance due to bus wiring.

Overcoming Issues Due to Bus Length

In addition to helping to expand the capacity of bus networks,embodiments according to this disclosure can help overcome issuesassociated with the impedance of the wiring in bus networks. In DALI busnetworks, for example, as bus length increases the wiring impedanceitself will begin to limit current (rather than the power supply coupledto the network), which in the event of a communication attempt by a node130 can result in the inability of other nodes to recognize saidcommunication attempts.

Designers of conventional DALI systems typically reduce the bus length,increase the wiring cross section, and/or reduce the number of deviceson the bus to prevent the effects associated with high wiring impedance.The DALI standard requires that nodes monitor the bus voltage to detectcommunication (that is, <6.5V is logical zero, >11.5V represents alogical one). In a conventional DALI system with excessive wiringimpedance, however, nodes may not be able to detect those levels whenother nodes attempt to communicate and short the bus. For example, along bus may have an impedance of 100 Ohms. Even if a device shorts thebus, the resulting current may be 165 mA using a typical DALI powersupply. Since the current limit of 250 mA is not exceeded, no voltagedrop occurs and no communication is visible to other nodes 130.

Embodiments of the present disclosure as described above, however, canhelp devices 130 detect communications between control devices 120 andnodes 130, and between the nodes 130 themselves, allowing for a varietyof features to be implemented in a DALI network, even one with arelatively long bus length. For example, by allowing all nodes 130 onthe bus 140 to see communications between other nodes 130 and a controldevice 120, communication collisions can be detected and avoided. Forexample, where node A has the same address as node B on the bus, theymay both attempt to respond simultaneously to a communication from acontrol device. Embodiments of this disclosure allow the control deviceand both nodes to detect an attempted response by both devices andidentify the source of the collision. This can be particularlyadvantageous during the initial setup of a bus network (when assigningaddresses to all nodes on a bus) to identify nodes with duplicateaddresses.

Embodiments of this disclosure can also aid in networks having busarbitration and/or multiple control devices. In such systems, a busarbiter may declare the bus free for asynchronous (event type) messages.Nodes then can initiate communication as in a multi-master situation butthey must be able to detect whether another node already commencedtransmission. Similarly, embodiments of the disclosure can aid inimplementing priority communication schemes. For example, DALI supportsa scheme where a window for prioritized messages is opened, with thehigher the priority of the message the earlier in the window it must betransmitted. Embodiments of the disclosure aid in allowing the bus to bemonitored such that lower priority messages are not transmitted later inthe window if a higher priority transmission is already in progress. Inother embodiments, nodes 130 may be configured to communicatesynchronously with each other.

FIG. 7 illustrates an exemplary case where a bus has a relatively highwiring impedance. In this case, an increase in current draw by a firstdevice 710 can result in a decrease in current by other devices 720,without substantially affecting the current draw on the bus as detectedby the power supply. In this example, a network is powered by a standardDALI bus of 22V with a 250 mA current limit. After 50 Ohm of wiringimpedance, a group of devices 720 collectively consume 220 mA. Afteranother 49 Ohm wiring impedance is an additional single device 710. Thegroup of devices 720 have approximately 11V of supply voltage (reflectedby an 11V drop across the 50 Ohm impedance), neglecting the draw of theright device. In this example, the group of devices 720 will have theirrespective capacitors charged to approx. 10.5V (11V less a diode drop),while the overall current draw of this bus network amounts to about 220mA steady state.

If device 710 attempts to communicate, it shorts the bus, causingcurrent flow through both the 50 Ohm and the 49 Ohm wiring impedance,and causing an additional drop across the 50 Ohm resistance. The voltageat junction A will drop and the group of devices 720 will have a highervoltage in their capacitors than supply voltage. Consequently, devices720 will stop drawing current from the bus, and all current will flowthrough the device 710 shorting the bus. The current draw of this caseamounts to 22V/99 Ohm=222 mA, which is very close to the “pre-short”condition and therefore making it difficult to determine when a deviceis attempting communication.

Embodiments of the present disclosure can help address the issuesdescribed above. In an embodiment, a control device 120 can be coupledto the power supply 110 to facilitate outgoing communication asdescribed above. The current supplied by the power supply 110 isanalyzed in order to detect a potential response to the control device120 by the nodes 130.

The current drawn by the devices 130 can be detected in any suitablemanner. For example, as described previously, the current may bemeasured and provided to a high pass filter, which filters out theslowly changing steady state current. The filter's output may becompared against a positive threshold and a negative threshold.Referring now to FIG. 8, which depicts a typical communications timingdiagram for DALI devices, a rapid increase in current drawn by a device130 will exceed the positive threshold, which must be lower than thecurrent limit of a standard DALI power supply, and indicates a node'sattempt to response (point C in FIG. 8). As the node releases the bus(point E in FIG. 8) the current will rapidly drop, thereby creating anegative pulse behind the high pass filter and triggering the negativethreshold.

In an embodiment, when a device 130 shorts the bus 140, the incrementalcurrent is detected by the power supply 110, which additionally dropsits output voltage, which can be detected by the devices 130 on bus 140as an indicator of communication between devices 130. Once a device 130releases its short, voltage will rise again, thereby appearing as alogical one to all devices 130 on the bus 140. Once the entire responsehas been transmitted by a device 130, as may be detected by a “bus idletimeout” or as may be evident by the command that had been sent, thepower supply 110 can resume providing power at the original currentlimit.

This approach can be used to actively control the power supply's 110voltage to make communication between two devices (120, 130) visible toother devices 130. If the power supply implements current fold-back,then changing its output voltage can automatically change its currentlimit as well. In alternate embodiments, the control device 120 need notnecessarily be coupled to the power supply 110. Instead, the powersupply can be configured to detected increases in current and eitherlower the voltage directly or indirectly by lowering the current limit,thereby allowing the communication to be visible by all nodes.

In embodiments of the disclosure, the power supply 110 and one or moredevices 130 may cooperate to lower the overall current consumed by thedevices 130 on the bus 140. In an embodiment, the power supply 110 isconfigured to lower its current limit to cooperate with devices 130 thathave input stages which include a rectifier and capacitor (or otherenergy storage device), such as the device 500 shown in FIG. 5.

In an embodiment, when the control device 120 expects a response from anode 130, it indicates to the power supply 110 to preemptively lower thecurrent limit by the power supply 110. Alternately, the power supply maybe configured to lower its output voltage directly (i.e., withoutreceiving an indicator from the control device 120) by detecting thecurrent drawn by the devices 130. In either case, the power supply 110lowers the bus voltage below the voltage in the nodes' 130 capacitorsand they will stop drawing current, thereby satisfying the new currentlimit in the power supply 110. Because the capacitors are charged to thebus nominal “high voltage” (logical one), the newly established busvoltage is just under the nominal voltage, and thus the reduction of thecurrent limit does not cause the bus voltage to drop significantly.Embodiments of this disclosure may be configured to operate at anysuitable voltage level. In an embodiment, voltage levels are about 22.5Vnormally, well above the minimum voltage for a logical one on a DALI busof 9.5V.

In an embodiment, the nodes 130 on the bus 140 may be configured tomonitor all communication on the bus 140, and actively lower theircurrent consumption whenever a response is expected. Nodes 130performing this functionality need not have the rectifier/capacitorinput stage described in FIG. 5, but can have any suitable design. Forexample the nodes 130 may include the opto-coupler input stage (shown inFIG. 4) that is commonly found in DALI nodes.

A device 130 may be configured to change its current draw in response toa command (e.g., received from the control device), a measuredelectrical characteristic (e.g., the voltage level of the power suppliedby the power supply via the bus), a detected communication between otherdevices 130 on the bus, or any other suitable event.

In an example of an embodiment, referring again to FIG. 7, the group ofdevices 720 can collectively reduce their current consumption asdescribed above. A control device (not shown) coupled to the powersupply transmits a command that expects a response from device 710. Inanticipation of the command, the group of devices 720 collectively lowertheir current consumption from 220 mA to 22 mA, for example. The powersupply detects the reduction in current consumption from 220 mA to 22mA, and, upon device 710 attempting to communicate, sees a rapidincrease in current consumption to 222 mA. This increase in currentconsumption from 22 mA to 222 mA is easily detectable by both the powersupply 110 and control device 120 (coupled to the power supply 110),allowing the current waveform to be interpreted and the node's 710response retrieved.

In yet another example, referring again to FIG. 7, the power supply 110can drop its current limit upon detection of a transmission attempt. Inthis example, after the group of devices 720 reduce their collectivecurrent consumption to 22 mA, and device 710 shorts the bus to create alogical zero, current increases to 222 mA. The power supply 110 detectsthe increase and lowers its current limit from 250 mA to 50 mA. Thepower supply 110 adjusts the output voltage in order to limit current to50 mA, which will settle to about 5V (50 mA*99 Ohm). This allows thenodes 710, 720 to see and interpret the voltage as a logical zero, evenin cases where there is significant impedance due to bus wiring. Inorder to return to a logical one, node 710 releases the short and thecurrent drops. The power supply 110, detecting that it is no longercurrent limiting, reverts back to a 250 mA limit, causing the busvoltage to rise.

Due to the effects of high wiring impedance on the communication, theDALI standard specifies a maximum wiring impedance for the bus, that is,the longer the bus run, the higher the wire cross section (wire gauge)that must be used. However, this requires different types of wiredepending on the length of a bus, in turn requiring more carefulinstallations, more products to stock, etc. and also costlier wire.Embodiments of the present disclosure can provide significant advantagesover conventional systems. For example, conventional DALI bus networksusing 18 AWG wire are only capable of a maximum length of about 570 ft.In an embodiment according to aspects of this disclosure, by contrast, aDALI bus network may be implemented using 18 AWG wire (the minimum gaugeunder DALI requirements) of up to a length of about 1500 ft, and iscapable of delivering sufficient power to more devices than theconventional 570 ft network.

The above-described embodiments may be implemented in any manner, suchas through hardware, software, or a combination of the two.Functionality implemented through software may be performed by anysuitable computer-based system. Such a software program may be stored onany computer-readable medium, such as floppy disks, hard disks, CD-ROMs,DVDs, any type of optical or magneti-optical disks, volatile ornon-volatile memory, and/or any other type of media suitable for storingelectronic instructions and capable of interfacing with a computingdevice. Methods according to embodiments of present invention mayoperate in conjunction with any type of computer system, such as apersonal computer (PC), server, cellular phone, personal digitalassistant (PDA), portable computer (such as a laptop), embeddedcomputing system, and/or any other type of computing device. Thecomputer system may include any number of computing devices connected inany manner, such as through a distributed network. The computer systemmay communicate and/or interface with any number of users and/or othercomputing devices to send and receive any suitable information in anymanner, such as via a local area network (LAN), cellular communication,radio, satellite transmission, a modem, the Internet, and/or the like.

The particular implementations shown and described above areillustrative of the invention and its best mode and are not intended tootherwise limit the scope of the present invention in any way. Indeed,for the sake of brevity, conventional data storage, data transmission,and other functional aspects of the systems may not be described indetail. Furthermore, the connecting lines shown in the various figuresare intended to represent exemplary functional relationships and/orphysical couplings between the various elements. Many alternative oradditional functional relationships or physical connections may bepresent in a practical system.

The term “non-transitory” is to be understood to remove only propagatingtransitory signals per se from the claim scope and does not relinquishrights to all standard computer-readable media that are not onlypropagating transitory signals per se. Stated another way, the meaningof the term “non-transitory computer-readable medium” should beconstrued to exclude only those types of transitory computer-readablemedia which were found in In Re Nuijten to fall outside the scope ofpatentable subject matter under 35 U.S.C. §101.

Benefits, other advantages, and solutions to problems have beendescribed herein with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any elements that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as critical, required, or essentialfeatures or elements of the disclosure. The scope of the disclosure isaccordingly to be limited by nothing other than the appended claims, inwhich reference to an element in the singular is not intended to mean“one and only one” unless explicitly so stated, but rather “one ormore.” Moreover, where a phrase similar to ‘at least one of A, B, and C’or ‘at least one of A, B, or C’ is used in the claims or specification,it is intended that the phrase be interpreted to mean that A alone maybe present in an embodiment, B alone may be present in an embodiment, Calone may be present in an embodiment, or that any combination of theelements A, B and C may be present in a single embodiment; for example,A and B, A and C, B and C, or A and B and C. Although the disclosureincludes a method, it is contemplated that it may be embodied ascomputer program instructions on a tangible computer-readable carrier,such as a magnetic or optical memory or a magnetic or optical disk. Allstructural, chemical, and functional equivalents to the elements of theabove-described exemplary embodiments that are known to those ofordinary skill in the art are expressly incorporated herein by referenceand are intended to be encompassed by the present claims. Moreover, itis not necessary for a device or method to address each and everyproblem sought to be solved by the present disclosure, for it to beencompassed by the present claims. Furthermore, no element, component,or method step in the present disclosure is intended to be dedicated tothe public regardless of whether the element, component, or method stepis explicitly recited in the claims. No claim element herein is to beconstrued under the provisions of 35 U.S.C. 112, sixth paragraph, unlessthe element is expressly recited using the phrase “means for.” As usedherein, the terms “comprises”, “comprising”, or any other variationthereof, are intended to cover a non-exclusive inclusion, such that aprocess, method, article, or apparatus that comprises a list of elementsdoes not include only those elements but may include other elements notexpressly listed or inherent to such process, method, article, orapparatus.

What is claimed is:
 1. A communication system comprising: an inputcomprising a positive terminal and a negative terminal to receive acontinuous voltage from a voltage generator, wherein the input iscoupled to an output comprising a positive terminal and a negativeterminal; a current regulator configure to limit the supply currentprovided by the voltage generator to the output to a maximum value; acommunication interface connected in parallel with the output, whereinthe electrical impedance between the positive terminal and the negativeterminal of the output is varied to transmit data; and a control circuitconfigured to detect the output voltage between the positive terminaland the negative terminal of the output, and to vary the maximum valueof the supply current provided by the voltage generator as a function ofthe detected output voltage.
 2. The communication system of claim 1,wherein the voltage generator is configured to provide a continuousvoltage, wherein the voltage generator is connected to the positiveterminal and the negative terminal of the input.
 3. The communicationsystem of claim 1, wherein the control circuit is configured to comparethe detected output voltage with a threshold, and in case the detectedoutput voltage is greater that the threshold, to set the maximum valueof the supply current provided by the voltage generator to the poweroutput to a first value, and in case the detected output voltage issmaller than the threshold, to set the maximum value of the supplycurrent provided by the voltage generator to the power output to asecond value, wherein the second value is smaller than the first value.4. The communication system of claim 1, wherein the communicationinterface is a transceiver.
 5. The communication system of claim 4,wherein the communication interface is a Digital Addressable LightingInterface.
 6. The communication system of claim 1, wherein the currentregulator is disposed between the positive terminal of the input and thepositive terminal of the output.
 7. The communication system of claim 1,wherein the current regulator comprises a measurement resistorconfigured to detect a voltage, which depends on the supply currentprovided by the voltage source, and wherein the current regulator isconfigured to limit the supply current provided by the voltage source asa function of the voltage detected by the measurement resistor.
 8. Thecommunication system of claim 7, wherein the control circuit isconfigured to vary the electrical resistance of the measurement resistoras a function of the detected output voltage.
 9. The communicationsystem of claim 1, further comprising: a device connected to the output,the device comprising a communication interface connected in parallelwith the output, wherein the device is configured to be powered via thepositive terminal and the negative terminal of the output.
 10. Alighting system comprising: a communication system, comprising: an inputcomprising a positive terminal and a negative terminal to receive acontinuous voltage from a voltage generator, wherein the input iscoupled to an output comprising a positive terminal and a negativeterminal; a current regulator configure to limit the supply currentprovided by the voltage generator to the output to a maximum value; acommunication interface connected in parallel with the output, whereinthe electrical impedance between the positive terminal and the negativeterminal of the output is varied to transmit data; and a control circuitconfigured to detect the output voltage between the positive terminaland the negative terminal of the output, and to vary the maximum valueof the supply current provided by the voltage generator as a function ofthe detected output voltage; and a power supply circuit configured topower a light source, wherein the power supply circuit comprises acommunication interface connected in parallel with the output, andwherein the communication interface of the power supply circuit isconfigured to receive configuration parameters from the communicationsystem and/or to transmit data that indicates the operation of the powersupply circuit and/or the light source to the communication system. 11.The lighting system of claim 10, wherein the voltage generator isconfigured to provide a continuous voltage, wherein the voltagegenerator is connected to the positive terminal and the negativeterminal of the input.
 12. The lighting system of claim 10, wherein thecontrol circuit is configured to compare the detected output voltagewith a threshold, and in case the detected output voltage is greaterthat the threshold, to set the maximum value of the supply currentprovided by the voltage generator to the power output to a first value,and in case the detected output voltage is smaller than the threshold,to set the maximum value of the supply current provided by the voltagegenerator to the power output to a second value, wherein the secondvalue is smaller than the first value.
 13. The lighting system of claim10, wherein the communication interface is a transceiver.
 14. Thelighting system of claim 13, wherein the communication interface is aDigital Addressable Lighting Interface.
 15. The lighting system of claim10, wherein the current regulator is disposed between the positiveterminal of the input and the positive terminal of the output.
 16. Thelighting system of claim 10, wherein the current regulator comprises ameasurement resistor configured to detect a voltage, which depends onthe supply current provided by the voltage source, and wherein thecurrent regulator is configured to limit the supply current provided bythe voltage source as a function of the voltage detected by themeasurement resistor.
 17. The lighting system of claim 16, wherein thecontrol circuit is configured to vary the electrical resistance of themeasurement resistor as a function of the detected output voltage. 18.The lighting system of claim 10, wherein the communication systemfurther comprises: a device connected to the output, the devicecomprising a communication interface connected in parallel with theoutput, wherein the device is configured to be powered via the positiveterminal and the negative terminal of the output.
 19. A method ofoperating a communication system, comprising: detecting a valueindicative of an output voltage between a positive terminal and anegative terminal of an output, wherein the output is coupled to aninput, wherein the input comprises a positive terminal and a negativeterminal to receive a continuous voltage from a voltage generator;providing, by the voltage generator, a supply current to the output; andvarying a maximum value of the supply current provided by the voltagegenerator as a function of the value indicative of the output voltage.